ST_Force3DM
ST_Force3DM returns a 3DM geometry of the input geometry.
For 2D geometries, the m
coordinates of the nonempty points in the output geometry are all set to 0
.
For 3DM geometries, a copy of the input geometry is returned.
For 3DZ geometries, the geometry is projected to the xyCartesian plane,
and the m
coordinates of the nonempty points in the output geometry are all set to 0
.
For 4D geometries, the geometry is projected to the xymCartesian space.
Empty points in the input geometry remain empty points in the output geometry.
Syntax
ST_Force3DM(geom)
Arguments
 geom

A value of data type
GEOMETRY
or an expression that evaluates to aGEOMETRY
type.
Return type
GEOMETRY
.
The spatial reference system identifier (SRID) value of the returned geometry is the SRID value of the input geometry.
If geom is null, then null is returned.
If geom is empty, then an empty geometry is returned.
Examples
The following SQL returns a 3DM geometry from a 3DZ geometry.
SELECT ST_AsEWKT(ST_Force3DM(ST_GeomFromText('MULTIPOINT Z(0 1 2, EMPTY, 2 3 4, 5 6 7)')));
st_asewkt

MULTIPOINT M ((0 1 0),EMPTY,(2 3 0),(5 6 0))